<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>query</title>
</head>
<body>
    <button>发送ajax</button>
    <script>
        const btn = document.querySelector('button');
        btn.onclick = function(){
            const xhr = new XMLHttpRequest();
            xhr.open('get','http://127.0.0.1/json');
            xhr.responseType = 'json';
            xhr.send();
            xhr.onreadystatechange = function(){
                if(xhr.readyState ===4){
                    if(xhr.status >=200 && xhr.status < 300){
                        console.log(xhr.response,typeof xhr.response);
                    }
                }
            }
        }
    </script>
</body>
</html>